Flash memory can retain the stored data even after power to the memory is removed, and allows data erasing and writing functions. With these advantages, the flash memory has been broadly applied in various electronic products. A conventional flash memory is divided into multiple memory blocks and each memory block is constituted by a number of memory cells, and each cell is used to store a bit data. The memory cell has a control gate, a floating gate, a source and a drain. The stored data in the memory cell is determined according to the storage amount of charges in the floating gate.
However, the typical memory cell is fabricated with two stacked polysilicon layers to be the control gate and the floating gate, which needs another polysilicon process in comparison with the manufacturing process of a typical metal-oxide-semiconductor (MOS) transistor of a logic circuit, so that the process is more complicated and the memory cell is hard to integrate with the manufacturing process of the logic circuit and thus must be fabricated separately.